Catalytic dehydrogenation of aliphatic nitriles



aliphatic straight and branch chained Patented Mar. 2, 1954 UNITED STATES PATENT] OFFICE CATALYTIC DEHYDROGENATION OF ALIPHATIC NITRILES La Vern H. Beckberger, to Sinclair Refining Co a corporation of Maine Markham, BL, assignor' mpany, New York, N. Y.,

3 Claims. (01. 260'465.9)

My invention relates to the catalytic dehydrogenation of aliphatic nitriles. More particularly, my invention is directed to the production of unsaturated nitriles by the catalytic dehydrogenation of aliphatic nitriles containing the same number of carbon atoms.

The dehydrogenation of aliphatic nitriles proceeds according to the primary reaction wherein R represents an aliphatic radical and R is a corresponding unsaturated radical. resents radicals such as ethyl, propyl, isopropyl, butyl, crotyl, amyl, octyl, lauryl, cetyl and other radicals susceptible to dehydrogenation of a saturated pair of adjacent carbon atoms.

'The dehydrogenation reaction is carried out in the vapor phase at elevated temperatures of the order of 1150 F., at low pressures of the order of 1 atmosphere, and in the presence of catalysts. Under such conditions the equilibrium is favorable to production of the unsaturated nitrile but reaction equilibrium is not approached. Many competing primary reactions and secondary reactions also take place causing the formation of large quantities of lower saturated nitriles, HCN, NH4CN, gaseous olefins and paraffins,'carbona ceous deposits, and, to some extent, polymerized products. Thus, in effecting the dehydrogenation reaction, there is a permanent and undesirable loss of reactant reducing the ultimate yield of the desired product.

My invention has as its principal object to improve the yield of the desired unsaturated nitrile but also accomplishes a significant reduction in the ratio of products to hydrogen product, and effectively suppresses the formation of hydrogen cyanide gas.

I have discovered that these ends may be attained by adding hydrogen cyanide gas to the R repnitrile feed before introducing the feed to the reaction catalyst. I prefer to employ a molar ratio of HCNznitrile of approximately 2:1. However, ratios as low as 1:10 are effective and there is no upper limit on the mole ratio of HCN to nitrile other than is dictated by practical considerations. One convenient method for accomplishing the purpose of my invention includes preparing a feed mixture of aliphatic nitrile and hydrogen cyanide which is subjected to dehydrogenation conditions. The reaction eflluent is readily fractionated and the hydrogen cyanide and unreacted nitrile recovered may be recycled with the feed mixture.

Many suitable catalysts have been prepared and utilized successfully in the dehydrogenation of nitriles. None however is capable of effecting complete conversion to equilibrium conditions even upon unduly protracted contact between the nitrile and catalyst. Many of the catalysts suc cessfully utilized, i. e. chromia-alumina, show extremely high rates of conversion, but are equally effective in promoting extraneous competing side reactions and secondary reactions such as cracking, rearrangement, and polymerization. Other catalysts showing similar rates of conversion are more successfully utilized because they are highly selective to the specific reaction. Two such catalysts are amorphous chromium oxide-copper oxide and amorphous chromium oxide supported on pumice. Other useful catalysts are those generally useful in dehydrogenation reactions. Specifically various non-reduci-ble metal oxides such as chromium oxide, alumina, molybdenum oxide, barium oxide, zinc oxide, magnesia and vanadia are useful. These catalysts have been found suitable in pelleted or finely divided form, in mixtures, as single component catalysts, or supports.

dependent My discovery is not related to nor upon any particular catalyst since the reaction involved is not so limited. However, it is generally necessary that a catalyst be not approached and the sole effect of temperature on the reaction is on rate. decreased pressures theoretically So also, while variations within the range of about 500 mm. Hg to 1500 mm. Hg have little effect on the relative proportions of the reaction effluents and on the reaction rates involved. I generally prefer to operate at nitrile partial pressures between 25 mm. Hg and 250 mm. Hg. I might also point out that high temperatures such as 1300 F. and

above, while increasing the reaction rate, have a greater effect on the reaction rates and equilibria of the principal competing primary and second- The choice of 1300 F. is rather arbitrary but it constitutes a practical upper limit on temperatures employed. Below about 950F. the rates are so reduced conversion impractical.

The suitable space velocity, or catalyst to feed ratio, will depend largely upon the nature of the catalyst employed and the manner of its handling. Such choice is a matter of individual preference and is readily variable. I prefer employing nitrile space velocities within the range prepared on inert or active give a more favorable equilibrium. I have found pressure as to render;

of about,lp to a or lfl v./v./hr .,t calcnlating the volume ofyi eecl: as in theliquid phase;

In order to illustrate the practice of my invention I have chosen the dehydrogenation of propionitrile but it will be understood by persons skilled in the art that the illustrationsiseapplii., cable to the dehydrogenation of other aliphatica nitriles having between 4 and 12. 1; more carbon atoms per molecule. The aliphaticgadical,may, be either branched or straight'chained, paraffin or olefin, but must possess saturated carbon to carbon linkages susceptible to dehydrogenation; at elevated temperatures in the presence of-=adehydrogenation catalyst. Generally, the carbon to carbon bond which is most susceptible to dehydrogenation is that between the second and m a e-$ 91 stems r m the itrile mtr een. ato s m ion tt lQQi S Pr m ry:

il watic b h e a on mtq uc q oni rile growing industrialimportance being usefulinthe 2 a li at re f; het c s ns. l s.- ii ii ib in e ma ui tu 'ofiimeetu a e wide mines a ide nds-st m y v i ysie r e i Q1Y sand-i he r s sl jharma t a edate qati sg w aimbt hs i e sandi r P 1Y ema e mgrphe s trqm um 03191 i asi epatsiasre ae atedee -as e w V fi l e se hrsimica id 1 91): s; i

new; QQ QL W wat r-v i t P91? QIlS. oi h l altqh, b e e-a d d; t his 1 Lil-W h freeu t h ls gl-ut oe wa swerv d then;- 8Q c; niorealco ol e -add di i n e em ll een r;

l. fe e ere-i qln se ers-t efieXeM- n m chanis s? p -a /5min teintwe in he l t on-1 he: ta d; 1 c r eed ifihf h @rsit na mu 'wa e m-week fie t. rmin a .c o q ate brp n ecipita e e-. e--

cipjitate was fllterc-ad ir we e e herwn nd he 3 F ke was b t-ghee .1 n par a ly rie ew; i ndenwn 'ons ii; sai midiin nally r s ees h mgez'e s t 0 resulting particles were black and vitreous naly e a lishedtha amzm mate 7. the ,total chromium in the dried amorphous ca'ta aly'st so prepared. was present; as he gavalent,

e ane pre entin t i en 1e chromium.

the catalyst, having ,a, particle siaeQof 8-14, mesh; was-placed in. au'eactor, PIOrpior itrile which-analyzed:

' ortion of we ht ers nt nnm -3":

Propionitrile aces sob tvmn rfle fli 3.1,

was blended with the hydrogen; cyanide in ratio of two I noles of hydrogen-cyanide t0- one- 60,, mole of the nitrile, calculatedas 'propionitrilez The blend was heated to1l -'F:-under-atinospheric pressure of -750- mm: Hg and was charged to the reactor containing the chromium 'gelcatalyst -at a space velocity oi 1.0 calculated on the -65,, propionitr-ile feed.

The identical procedure was repeated-"twice;- using-iresh portions of catalyst irom;thesam-e I batch and three additional runs -iwere made again employing the same-propionitrile space ve- 70, locityand partial pressure, and employing each timev =fresh '.charges of the catalyst but omitting the. hydrogen cyanidein the-reed. 3

The runs, employing the hydrogen--;cyanidq -in the 1 .feed i-exhibited :no production of- -hydmgen=-fl5 cyan dels s m HQNa e ne eco e in heee d ed tem han w s har ngthe feed. The runs charged with a nitrile feed only, however, exhibited a I-ICN production of about 40 mole per cent based on the production of acrylonitrile; thus. representing a. permanent lcs fofenitrile reactant of a high order.

Again the,runs ernploying the hydrogen cyani :tril feed reduced acrylonitrile, on the has of -the pg p on trile feed, equivalent to that producedwhen no hydrogen cyanide was employediin theieed; but utilized 15 to 20 per cent by "Weight less propionitrile. That is, the ratio of acrylonitrile to propionitrile reacted, when the feed contained hydrogen cyanide, was about Z9l-p r.p n f.,the same. at awhe athein t il e d ;.was-., m l e i hout h dro en. at c anide-.. 'rnusthe, ros s gpigmr nvent on. epresents. ore ve i icie.. t: 1 .11 nho r pi nitri ereact: nt. w ich? npwmrrdal,g rac ceivill resu considerable savings and econorn Mc gore a ha am inatqimy in,- vention ubstantiall use e dl netxqdu t onl of normally gaseous olefin and paraffin products such as methane;- ethane; ethylene, and prop lenei he. molan atio thaw-sh m flnen iydrp eefe s-S Qih d o arh iseas -was. ub:: antia l eetn em: F v, e' rthe ro sems,- lay d hn m en an ee itr le e d, b w eathen i henc man-mi es lwerei e nta nt hat-feeds. in a t sanimd pationi l dlthat the process of my inventio eiiefitiyelysup pr sses eompe ngreaciiens.i ith l emt entlq s ileeq antinnere verable rmtnhe atalyt a h dmaen t om f.. iphatio i esia{Me usa pqrresnqn m tuns n t' dt it le -fl yconta t n -a iphat c; e true t zarsoli r-ldhydr na onio talvsteinat timnmeat a ltemneratur i it mheran e". iehguwfimttqb u QDii nd re nven nel eun a urat dmania oductlirQm-men eaea one fiu nti he mnm mentw bichl co -p xin a-m e Lc ii ist ne se tiall e resser-L mmas i i -tgt en-aliiih le; nitrii i ha la l a ot t sl o n bram ea mt il.=+ e natfl ash lo oneatras mm n et i he n t inb9u t95.flt o ebou ilwflfe eq veriaathe rbnitril pro uct-f o t e etioas luentath a rxoremen w ch, o, prises mixing a material consisting essentially oi, hydro n "cyanide th vthe, propio r lei heimolartr liant hvdmsenyc anid t rp opioee itri eb ina t 1 t,-. .=1 .Q: v

3;,A r cessi r th a e e d at sleim a l eepte cn q he rea it es smilenten nre .lucticnlof ,acr lonitrilei, .in-- h shh tlrl ee ecyanidei i nitin ar i e s r e ii qmi s d eii de rsmcesfiited: i tha laot t i atent; UNITEDeSTATESf enemas-1; 

1. IN THE CATALYTIC DEHYDROGENATION OF ALIPHATIC NITRILES TO PRODUCE CORRESPONDING UNSATURATED NITRILES BY CONTACTING AN ALIPHATIC NITRILE WITH A SOLID DEHYDROGENATION CATALYST IN A REACTION ZONE AT A TEMPERATURE WITHIN THE RANGE OF ABOUT 950* F. TO ABOUT 1300* F. AND RECOVERING THE UNSATURATED NITRILE PRODUCT FROM THE REACTION EFFLUENT, THE IMPROVEMENT WHICH COMPRISES MIXING A MATERIAL CONSISTING ESSENTIALLY OF HYDROGEN CYANIDE WITH THE ALIPHATIC NITRILE FEED, THE MOLAR RATIO OF HYDROGEN CYANIDE TO NITRILE BEING AT LEAST 1:10. 